1. Field of the Invention
The present invention relates to a pixel position specifying method, a method of correcting image offset, and an image forming device. In particular, the present invention relates to, in an image forming device equipped with a plurality of exposure heads, a pixel position specifying method which can specify with high accuracy the positions of connecting pixels at exposure heads even if relative positions among exposure heads change, and a method of correcting image offset which can form an image of high quality in which junctures (“seams”) are not conspicuous, and an image forming device which can correct offset between images of exposure heads in accordance with the method of correcting image offset.
2. Description of the Related Art
Conventionally, various exposure devices, which carry out image exposure by a light beam modulated in accordance with image data by using spatial light modulators (SLMs) such as digital micromirror devices (DMDs) or the like, have been proposed as examples of image recording devices. (See, for example, Larry J. Hornbeck, “Digital Light Processing and MEMS: Reflecting the Digital Display Needs of the Networked Society”, THE INTERNATIONAL SOCIETY FOR OPTICAL ENGINEERING, Proceedings of SPIE, Volume: 2783, 8/1996, pp. 2-11, and W. E. Nelson and Robit L. Bhuva, “Digital Micromirror Device Imaging Bar for Hard Copy”, THE INTERNATIONAL SOCIETY FOR OPTICAL ENGINEERING, Proceedings of SPIE, Volume: 2413, 4/1995, pp. 58-65.) A DMD is structured, for example, by providing a large number of extremely small micromirrors on respective memory cells such as SRAMs, and varies the angles of the reflecting surfaces of the micromirrors by static electricity due to charges accumulated in the respective memory cells. When carrying out image drawing in actuality, in a state in which image data is written to the respective SRAMs, the respective micromirrors are reset and set to predetermined angles, and the directions of reflection of the light are made to be desired directions.
One example of a field of application of exposure devices is the manufacturing of panels of, for example, liquid crystal displays and the like.
A multi-head exposure device is an example of an exposure device for the manufacturing of panels. In the multi-head exposure device, a plurality of exposure heads having DMDs are arranged along a direction perpendicular to the direction of feeding a photosensitive material such as a substrate or the like, in order to widen the range of exposure.
In the multi-head exposure device, the relative positions among the respective heads are adjusted with high accuracy to the extent that junctures do not cause problems in actual practice.
However, in recent years, as the degree of integration of substrates has increased, even higher resolutions have come to be demanded. Therefore, the allowable value of the offset between the relative positions of the images corresponding to the respective exposure heads has decreased.
Moreover, in an exposure head, a large number of optical members and mechanism members and the like are used from the light source to the imaging surface. Therefore, due to thermal expansion and thermal contraction of the respective members due to changes in temperature, and due to the accumulation of changes over time due to usage over a long period of time, offset or overlapping to an extent which cannot be ignored arises at the portions of the images which are junctures of the respective exposure heads, and a problem arises in that the image quality deteriorates.
A method has been proposed in which, in a multibeam exposure device used for purposes similar to those of the above-described multi-head exposure device, the positions of respective beams are detected by position detecting elements such as position sensing devices (PSDs) or quartered detectors or the like, and the offset between the images formed by the respective beams is corrected (see, for example, Japanese Patent Application (JP-A) No. 10-31170).
However, the intervals between the exposure heads in a multi-head exposure device are much larger than the intervals between adjacent beams. Therefore, it is difficult to apply the aforementioned method to a multi-head exposure device.